Voltage tracking circuit and method of operating the same

ABSTRACT

A voltage tracking circuit includes a first, second, third and fourth transistor. The first transistor is in a first well, and includes a first gate, a first drain and a first source coupled to a first voltage supply. The second transistor includes a second gate, a second drain and a second source. The second source is coupled to the first drain. The second gate is coupled to the first gate and the pad voltage terminal. The third transistor includes a third gate, a third drain and a third source. The fourth transistor includes a fourth gate, a fourth drain and a fourth source. The fourth drain is coupled to the third source. The fourth source is coupled to the pad voltage terminal. At least the third transistor is in a second well different from the first well, and is separated from the first well in a first direction.

PRIORITY CLAIM AND CROSS-REFERENCE

This application claims the benefit of U.S. Provisional Application No. 62/954,924, filed Dec. 30, 2019, which is herein incorporated by reference in its entirety.

BACKGROUND

The recent trend in miniaturizing integrated circuits (ICs) has resulted in smaller devices which consume less power, yet provide more functionally at higher speeds than before. The miniaturization process has also increased the devices' susceptibility to electrostatic discharge (ESD) events due to various factors, such as thinner dielectric thicknesses and associated lowered dielectric breakdown voltages. ESD is one of the causes of electronic circuit damage and is also one of the considerations in semiconductor advanced technology.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1A is a schematic diagram of an integrated circuit, in accordance with some embodiments.

FIG. 1B is a cross-sectional view of integrated circuit, in accordance with some embodiments.

FIG. 2A is a schematic diagram of an integrated circuit, in accordance with some embodiments.

FIG. 2B is a cross-sectional view of integrated circuit, in accordance with some embodiments.

FIG. 3A is a circuit diagram of an integrated circuit, in accordance with some embodiments.

FIG. 3B is a circuit diagram of an equivalent circuit of integrated circuit, in accordance with some embodiments.

FIG. 3C is a cross-sectional view of integrated circuit, in accordance with some embodiments.

FIG. 4A is a circuit diagram of an integrated circuit, in accordance with some embodiments.

FIG. 4B is a circuit diagram of an equivalent circuit of integrated circuit, in accordance with some embodiments.

FIG. 4C is a cross-sectional view of integrated circuit, in accordance with some embodiments.

FIG. 5A is a circuit diagram of an integrated circuit, in accordance with some embodiments.

FIG. 5B is a circuit diagram of an equivalent circuit of integrated circuit, in accordance with some embodiments.

FIG. 5C is a cross-sectional view of integrated circuit, in accordance with some embodiments.

FIG. 6A is a circuit diagram of an integrated circuit, in accordance with some embodiments.

FIG. 6B is a circuit diagram of an equivalent circuit of integrated circuit, in accordance with some embodiments.

FIG. 6C is a cross-sectional view of integrated circuit, in accordance with some embodiments.

FIG. 7A is a circuit diagram of an integrated circuit, in accordance with some embodiments.

FIG. 7B is a circuit diagram of an integrated circuit, in accordance with some embodiments.

FIG. 7C is a circuit diagram of an integrated circuit, in accordance with some embodiments.

FIG. 7D is a circuit diagram of an integrated circuit, in accordance with some embodiments.

FIG. 8 is a circuit diagram of a control logic circuit, in accordance with some embodiments.

FIG. 9 is a flowchart of a method of operating a circuit, such as the integrated circuit of FIG. 1A-1B, 2A-2B, 3A-3C, 4A-4C, 5A-5C, 6A-6C, 7A-7D or 8, in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides different embodiments, or examples, for implementing features of the provided subject matter. Specific examples of components, materials, values, steps, arrangements, or the like, are described below to simplify the present disclosure. These are, of course, merely examples and are not limiting. Other components, materials, values, steps, arrangements, or the like, are contemplated. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

In accordance with some embodiments, a voltage tracking circuit includes a first transistor, a second transistor, a third transistor and a fourth transistor. In some embodiments, the first transistor and second transistor are coupled to each other in a stacked structure, and the third transistor and the fourth transistor are coupled to each other in another stacked structure.

In some embodiments, each of a first gate terminal of the first transistor, a third gate terminal of the third transistor and a pad voltage terminal are coupled to each other, and configured to receive a pad voltage. In some embodiments, each of a second gate terminal of the second transistor, a fourth gate terminal of the fourth transistor and a first voltage supply are coupled to each other, and configured to receive a supply voltage.

In some embodiments, the first transistor is in a first well, and at least the third transistor is in a second well different from the first well. In some embodiments, the second well is separated from the first well in a first direction.

In some embodiments, by positioning at least the first transistor and the third transistor in corresponding separate wells, the voltage tracking circuit has better ESD immunity and occupies less area than other approaches.

Integrated Circuit

FIG. 1A is a schematic diagram of an integrated circuit 100A, in accordance with some embodiments.

Integrated circuit 100A comprises P-type Metal Oxide Semiconductor (PMOS) transistors M1, M2, M3 and M4 coupled to a voltage supply VDD and a pad terminal PAD. In some embodiments, integrated circuit 100A corresponds to a pad voltage tracking circuit configured to track a voltage from the pad terminal PAD. In some embodiments, the pad terminal PAD corresponds to an input/output (IO) pad, a voltage supply pad (e.g., VDD), a reference voltage supply (e.g., VSS), or the like.

Each PMOS transistor M1, M2, M3 and M4 is positioned in a corresponding well NW4, NW1, NW3 and NW2. For example, PMOS transistor M1 is positioned in a well NW4, PMOS transistor M2 is positioned in a well NW1, PMOS transistor M3 is positioned in a well NW3, and PMOS transistor M4 is positioned in a well NW2. At least well NW4, NW1, NW3 or NW2 includes an n-type dopant impurity, and is referred to as an N-Well. In some embodiments, at least well NW4, NW1, NW3 or NW2 includes a p-type dopant impurity, and is referred to as a P-Well.

PMOS transistor M1 is positioned in the well NW4. PMOS transistor M1 includes a gate terminal, a drain terminal, a source terminal, and a body terminal. The source terminal of PMOS transistor M1 is coupled to at least the first voltage supply VDD. The gate terminal of PMOS transistor M1 is coupled to at least the pad terminal PAD and is configured to receive a pad voltage (not labelled). The body terminal of PMOS transistor M1 is coupled to the well NW4.

PMOS transistor M2 is positioned in the well NW1. PMOS transistor M2 includes a gate terminal, a drain terminal, a source terminal, and a body terminal. The source terminal of PMOS transistor M2 is coupled to at least the pad terminal PAD and is configured to receive a pad voltage (not labelled). The gate terminal of PMOS transistor M2 is coupled to at least the voltage supply VDD, and is configured to receive the supply voltage (not labelled). The body terminal of PMOS transistor M2 is coupled to the well NW1.

PMOS transistor M3 is positioned in the well NW4. PMOS transistor M1 includes a gate terminal, a drain terminal, a source terminal, and a body terminal. The source terminal of PMOS transistor M3 is coupled to the drain terminal of PMOS transistor M1. Each of the gate terminal of PMOS transistor M3, the gate terminal of PMOS transistor M1 and the source terminal of PMOS transistor M2 are coupled together, and are also coupled to the pad terminal PAD. The gate terminal of PMOS transistor M3 and the gate terminal of PMOS transistor M1 are configured to receive the pad voltage (not labelled) from the pad terminal PAD. The body terminal of PMOS transistor M3 is coupled to the well NW3.

PMOS transistor M4 is positioned in the well NW2. PMOS transistor M4 includes a gate terminal, a drain terminal, a source terminal, and a body terminal. The source terminal of PMOS transistor M4 is coupled to the drain terminal of PMOS transistor M2. The drain terminal of PMOS transistor M4 and the drain terminal of PMOS transistor M3 are coupled together, and are electrically floating. Each of the gate terminal of PMOS transistor M2, the gate terminal of PMOS transistor M4 and the source terminal of PMOS transistor M1 are coupled together, and are also coupled to the voltage supply VDD. The gate terminal of PMOS transistor M4 and the gate terminal of PMOS transistor M2 are configured to receive the supply voltage (not labelled) from the voltage supply VDD. The body terminal of PMOS transistor M4 is coupled to the well NW2.

Other transistor types or other numbers of transistors in at least integrated circuit 100A-100B (FIG. 1B), 200A-200B (FIGS. 2A-2B), 300A-300C (FIGS. 3A-3C), 400A-400C (FIGS. 4A-4C), 500A-500C (FIGS. 5A-5C), 600A-600C (FIGS. 6A-6C) or 700A-700D (FIGS. 7A-7D) are within the scope of the present disclosure.

In some embodiments, by positioning PMOS transistors M1, M2, M3 and M4 in corresponding separate wells NW4, NW1, NW3 and NW2, integrated circuit 100A-100B has better ESD immunity and occupies less area than other approaches.

FIG. 1B is a cross-sectional view of integrated circuit 100B, in accordance with some embodiments. Integrated circuit 100B is an embodiment of integrated circuit 100A.

Components that are the same or similar to those in one or more of FIGS. 1A-1B and 2A-8 (shown below) are given the same reference numbers, and detailed description thereof is thus omitted.

Integrated circuit 100B comprises a substrate 102. In some embodiments, substrate 102 is a p-type substrate. In some embodiments, substrate 102 is an n-type substrate. In some embodiments, substrate 102 includes an elemental semiconductor including silicon or germanium in crystal, polycrystalline, or an amorphous structure; a compound semiconductor including silicon carbide, gallium arsenic, gallium phosphide, indium phosphide, indium arsenide, and indium antimonide; an alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and GaInAsP; another suitable material; or combinations thereof. In some embodiments, the alloy semiconductor substrate has a gradient SiGe feature in which the Si and Ge composition change from one ratio at one location to another ratio at another location of the gradient SiGe feature. In some embodiments, the alloy SiGe is formed over a silicon substrate. In some embodiments, first substrate 102 is a strained SiGe substrate. In some embodiments, the semiconductor substrate has a semiconductor on insulator structure, such as a silicon on insulator (SOI) structure. In some embodiments, the semiconductor substrate includes a doped epi layer or a buried layer. In some embodiments, the compound semiconductor substrate has a multilayer structure, or the substrate includes a multilayer compound semiconductor structure.

Integrated circuit 100B further comprises wells NW1, NW2, NW3 and NW4 in substrate 102. In some embodiments, at least well NW1, NW2, NW3 or NW4 includes a dopant impurity type opposite of the substrate type. In some embodiments, at least well NW1, NW2, NW3 or NW4 includes an n-type dopant impurity, and substrate is a p-type substrate. In some embodiments, at least well NW1, NW2, NW3 or NW4 includes a p-type dopant impurity, and substrate is an n-type substrate.

At least well NW1, NW2, NW3 or NW4 extends in a first direction X. Each of wells NW1, NW2, NW3 or NW4 is separated from another of wells NW1, NW2, NW3 or NW4 in the first direction X. In some embodiments, at least well NW4, NW3, NW2 or NW1 is referred to as a body of corresponding PMOS transistor M1, M3, M4 or M2.

Integrated circuit 100B further comprises regions 104 a, 104 b, 104 c and 104 d. Region 104 a, 104 b, 104 c or 104 d is within corresponding well NW4, NW3, NW2 or NW1. In some embodiments, at least region 104 a, 104 b, 104 c or 104 d includes an n-type dopant impurity. In some embodiments, at least region 104 a, 104 b, 104 c or 104 d includes a p-type dopant impurity. In some embodiments, region 104 a, 104 b, 104 c or 104 d is connected to a corresponding body terminal of corresponding PMOS transistor M1, M3, M4 or M2.

Integrated circuit 100B further comprises gates 106 a, 106 b, 106 c and 106 d. Gate 106 a, 106 b, 106 c or 106 d is above corresponding well NW4, NW3, NW2 or NW1. In some embodiments, gate 106 a, 106 b, 106 c or 106 d is a corresponding gate of corresponding PMOS transistor M1, M3, M4 or M2. For ease of illustration, gates 106 a and 106 b are not shown as being coupled to each other or other elements, and gates 106 c and 106 d are not shown as being coupled to each other or other elements.

Integrated circuit 100B further comprises implant regions 108 a, 108 b, 108 c and 108 d. Implant region 108 a, 108 b, 108 c or 108 d is within corresponding well NW4, NW3, NW2 or NW1. In some embodiments, at least implant region 108 a, 108 b, 108 c or 108 d includes a dopant impurity type opposite of the dopant impurity type in the corresponding well NW4, NW3, NW2 or NW1. In some embodiments, at least implant region 108 a, 108 b, 108 c or 108 d includes a p-type dopant impurity. In some embodiments, at least implant region 108 a, 108 b, 108 c or 108 d includes an n-type dopant impurity. In some embodiments, implant region 108 a or 108 b is the corresponding source terminal of corresponding PMOS transistor M1 or M3. In some embodiments, implant region 108 c or 108 d is the corresponding drain terminal of corresponding PMOS transistor M4 or M2.

Integrated circuit 100B further comprises implant regions 110 a, 110 b, 110 c and 110 d. Implant region 110 a, 110 b, 110 c or 110 d is within corresponding well NW4, NW3, NW2 or NW1. In some embodiments, at least implant region 110 a, 110 b, 110 c or 110 d includes a dopant impurity type opposite of the dopant impurity type in the corresponding well NW4, NW3, NW2 or NW1. In some embodiments, at least implant region 110 a, 110 b, 110 c or 110 d includes a p-type dopant impurity. In some embodiments, at least implant region 110 a, 110 b, 110 c or 110 d includes an n-type dopant impurity. In some embodiments, implant region 110 a or 110 b is the corresponding drain terminal of corresponding PMOS transistor M1 or M3. In some embodiments, implant region 110 c or 110 d is the corresponding source terminal of corresponding PMOS transistor M4 or M2.

Implant region 110 a is electrically coupled to implant region 108 b and corresponds to the connection between the drain terminal of PMOS transistor M1 and the source terminal of PMOS transistor M3 of FIG. 1A. Implant region 110 b is electrically coupled to implant region 108 c and corresponds to the connection between the drain terminal of PMOS transistor M3 and the drain terminal of PMOS transistor M4 of FIG. 1A. Implant region 110 c is electrically coupled to implant region 108 d and corresponds to the connection between the drain terminal of PMOS transistor M2 and the source terminal of PMOS transistor M4 of FIG. 1A.

A parasitic pnp transistor 112 a, 112 b, 112 c or 112 d is formed by corresponding well NW4, NW3, NW2 or NW1, corresponding implant region 108 a, 108 b, 108 c or 108 d and corresponding implant region 110 a, 110 b, 110 c or 110 d. For example, the well NW4 forms a base of parasitic pnp transistor 112 a, the implant region 108 a forms an emitter of parasitic pnp transistor 112 a and region 110 a forms a collector of parasitic pnp transistor 112 a. Similarly, the well NW3 forms a base of parasitic pnp transistor 112 b, the implant region 108 b forms an emitter of parasitic pnp transistor 112 b and region 110 b forms a collector of parasitic pnp transistor 112 a. Similarly, the well NW2 forms a base of parasitic pnp transistor 112 c, the implant region 108 c forms a collector of parasitic pnp transistor 112 c and region 110 c forms an emitter of parasitic pnp transistor 112 a. Similarly, the well NW1 forms a base of parasitic pnp transistor 112 d, the implant region 108 d forms a collector of parasitic pnp transistor 112 d and region 110 d forms an emitter of parasitic pnp transistor 112 d. In some embodiments, at least parasitic pnp transistor 112 a, 112 b, 112 c or 112 d is a parasitic bipolar junction transistor (BJT).

In some embodiments, at least parasitic pnp transistor 112 a, 112 b, 112 c or 112 d is configured to provide a current path for an ESD event. In some embodiments, the ESD event corresponds to a voltage of the pad terminal PAD being greater than a voltage of the supply voltage VDD. In some embodiments, at least parasitic pnp transistor 112 a, 112 b, 112 c or 112 d is configured to block a current path for the ESD event.

In some embodiments, by positioning PMOS transistors M1, M2, M3 and M4 in corresponding separate wells NW4, NW1, NW3 and NW2, integrated circuit 100B has better ESD immunity and occupies less area than other approaches.

FIG. 2A is a schematic diagram of an integrated circuit 200A, in accordance with some embodiments. Integrated circuit 200A is a variation of integrated circuit 100A, and similar detailed description is therefore omitted. For example, integrated circuit 200A illustrates an example of where additional PMOS transistors M5 and M6 are utilized in the stacked PMOS configuration of the PAD voltage tracking circuit.

In comparison with integrated circuit 100A of FIG. 1A, integrated circuit 200A further includes PMOS transistors M5 and M6 and corresponding wells NW5 and NW6.

PMOS transistor M5 or M6 is positioned in corresponding well NW5 or NW6. For example, PMOS transistor M5 is positioned in a well NW5, and PMOS transistor M6 is positioned in a well NW6. At least well NW5 or NW6 includes an n-type dopant impurity. In some embodiments, at least well NW5 or NW6 includes a p-type dopant impurity.

PMOS transistor M5 includes a gate terminal, a drain terminal, a source terminal, and a body terminal. The source terminal of PMOS transistor M5 is coupled to the drain terminal of PMOS transistor M3 in FIG. 2A. Each of the gate terminal of PMOS transistor M5, the gate terminal of PMOS transistor M1, the gate terminal of PMOS transistor M3 and the source terminal of PMOS transistor M2 are coupled together in FIG. 2A, and are also coupled to the pad terminal PAD. The gate terminal of PMOS transistor M5 is configured to receive the pad voltage (not labelled) from the pad terminal PAD. The body terminal of PMOS transistor M5 is coupled to the well NW5.

PMOS transistor M6 includes a gate terminal, a drain terminal, a source terminal, and a body terminal. The source terminal of PMOS transistor M6 is coupled to the drain terminal of PMOS transistor M4 in FIG. 2A. The drain terminal of PMOS transistor M6 and the drain terminal of PMOS transistor M5 are coupled together, and are electrically floating. Each of the gate terminal of PMOS transistor M6, the gate terminal of PMOS transistor M2, the gate terminal of PMOS transistor M4 and the source terminal of PMOS transistor M1 are coupled together in FIG. 2A, and are also coupled to the voltage supply VDD. The gate terminal of PMOS transistor M6 is configured to receive the supply voltage (not labelled) from the voltage supply VDD. The body terminal of PMOS transistor M6 is coupled to the well NW6.

In some embodiments, by positioning PMOS transistors M1, M2, M3, M4, M5 and M6 in corresponding separate wells NW4, NW1, NW3, NW2, NW5 and NW6, integrated circuit 200A-200B has better ESD immunity and occupies less area than other approaches.

FIG. 2B is a cross-sectional view of integrated circuit 200B, in accordance with some embodiments. Integrated circuit 200B is an embodiment of integrated circuit 200A.

Integrated circuit 200B is a variation of integrated circuit 100B, and similar detailed description is therefore omitted. For example, integrated circuit 100B illustrates an example of where additional PMOS transistors M5 and M6 are utilized in the stacked PMOS configuration of the PAD voltage tracking circuit (e.g., integrated circuit 100A of FIG. 1A).

In comparison with integrated circuit 100B of FIG. 1B, integrated circuit 200B further includes PMOS transistors M5 and M6 in corresponding wells NW5 and NW6.

In comparison with integrated circuit 100B of FIG. 1B, integrated circuit 200B further includes wells NW5 and NW6, regions 204 e and 204 f, gates 206 e and 206 f, implant regions 208 e and 208 f, and implant regions 210 e and 210 f.

Wells NW5 and NW6 are in substrate 102. In some embodiments, at least well NW5 or NW6 includes a dopant impurity type opposite of the substrate type. In some embodiments, at least well NW5 or NW6 includes an n-type dopant impurity, and substrate is a p-type substrate. In some embodiments, at least well NW5 or NW6 includes a p-type dopant impurity, and substrate is an n-type substrate.

At least well NW5 or NW6 extends in a first direction X. Each of wells NW1, NW2, NW3, NW4, NW5 or NW6 is separated from another of wells NW1, NW2, NW3, NW4, NW5 or NW6 in the first direction X. In some embodiments, at least well NW5 or NW6 is referred to as a body of corresponding PMOS transistor M5 or M6.

Region 204 e or 204 f is within corresponding well NW5 or NW6. In some embodiments, at least region 204 e or 204 f includes an n-type dopant impurity. In some embodiments, at least region 204 e or 204 f includes a p-type dopant impurity. In some embodiments, region 204 e or 204 f is connected to a corresponding body terminal of corresponding PMOS transistor M5 or M6.

Gate 206 e or 206 f is above corresponding well NW5 or NW6. In some embodiments, gate 206 e or 206 f is a corresponding gate of corresponding PMOS transistor M5 or M6. For ease of illustration, gates 106 a, 106 b and 206 e are not shown as being coupled to each other or other elements, and gates 106 c, 106 d and 206 f are not shown as being coupled to each other or other elements.

Implant region 208 e or 208 f is within corresponding well NW5 or NW6. In some embodiments, at least implant region 208 e or 208 f includes a dopant impurity type opposite of the dopant impurity type in the corresponding well NW5 or NW6. In some embodiments, at least implant region 208 e or 208 f includes a p-type dopant impurity. In some embodiments, at least implant region 208 e or 208 f includes an n-type dopant impurity. In some embodiments, implant region 208 e is the source terminal of PMOS transistor M5. In some embodiments, implant region 208 f is the drain terminal of PMOS transistor M6.

Implant region 210 e or 210 f is within corresponding NW5 or NW6. In some embodiments, at least implant region 210 e or 210 f includes a dopant impurity type opposite of the dopant impurity type in the corresponding well NW5 or NW6. In some embodiments, at least implant region 210 e or 210 f includes a p-type dopant impurity. In some embodiments, at least implant region 210 e or 210 f includes an n-type dopant impurity. In some embodiments, implant region 210 e is the drain terminal of PMOS transistor M5. In some embodiments, implant region 210 f is the source terminal of PMOS transistor M6.

In comparison with integrated circuit 100B of FIG. 1B, implant region 110 b of FIG. 2B is not electrically coupled to implant region 108 c.

Implant region 110 b of FIG. 2B is electrically coupled to implant region 208 e, and corresponds to the connection between the drain terminal of PMOS transistor M3 and the source terminal of PMOS transistor M5 of FIG. 2A. Implant region 108 c of FIG. 2B is electrically coupled to implant region 210 f, and corresponds to the connection between the drain terminal of PMOS transistor M4 and the source terminal of PMOS transistor M6 of FIG. 2A. Implant region 210 e is electrically coupled to implant region 208 f and corresponds to the connection between the drain terminal of PMOS transistor M5 and the drain terminal of PMOS transistor M6 of FIG. 2A.

A parasitic pnp transistor 212 e or 212 f is formed by corresponding well NW5 or NW6, corresponding implant region 208 e or 208 f and corresponding implant region 210 e or 210 f. For example, the well NW5 forms a base of parasitic pnp transistor 212 e, the implant region 208 e forms an emitter of parasitic pnp transistor 212 e and region 210 e forms a collector of parasitic pnp transistor 212 e. Similarly, the well NW6 forms a base of parasitic pnp transistor 212 f, the implant region 208 f forms a collector of parasitic pnp transistor 212 f and region 210 f forms an emitter of parasitic pnp transistor 212 f In some embodiments, at least parasitic pnp transistor 112 a, 112 b, 112 c, 112 d, 212 e or 212 f is a parasitic BJT.

In some embodiments, at least parasitic pnp transistor 112 a, 112 b, 112 c, 112 d, 212 e or 212 f is configured to provide a current path for an ESD event. In some embodiments, at least parasitic pnp transistor 112 a, 112 b, 112 c, 112 d, 212 e or 212 f is configured to block a current path for the ESD event.

In some embodiments, by positioning PMOS transistors M1, M2, M3, M4, M5 or M6 in corresponding separate wells NW4, NW1, NW3, NW2, NW5 or NW6, integrated circuit 200B has better ESD immunity and occupies less area than other approaches. In some embodiments, by having additional PMOS transistors M1, M2, M3, M4, M5 or M6 positioned in corresponding additional separate wells NW4, NW1, NW3, NW2, NW5 or NW6, integrated circuit 200B has better ESD immunity than other approaches with less transistors positioned in corresponding wells.

FIG. 3A is a circuit diagram of an integrated circuit 300A, in accordance with some embodiments. FIG. 3B is a circuit diagram of an equivalent circuit 300B of integrated circuit 300A, in accordance with some embodiments. FIG. 3C is a cross-sectional view of integrated circuit 300A, in accordance with some embodiments.

Integrated circuit 300A is an embodiment of integrated circuit 100A of FIG. 1A.

Integrated circuit 300A comprises PMOS transistors M1, M2, M3 and M4 coupled to the voltage supply VDD and the pad terminal PAD.

In comparison with integrated circuit 100A of FIG. 1A, PMOS transistor M1 is positioned in a well 320 a (FIG. 3C), and PMOS transistors M2, M3 and M4 are positioned in a well 320 b (FIG. 3C) different from well 320 a.

The body terminal of PMOS transistor M1 and the source terminal of PMOS transistor M1 are coupled together, and are further coupled to the first voltage supply VDD. By coupling the body terminal of PMOS transistor M1, the source terminal of PMOS transistor M1 and the voltage supply VDD, the parasitic PNP transistor 112 a of FIG. 1A is changed to a parasitic diode D1 (FIG. 3B).

PMOS transistors M2, M3 and M4 are positioned in a same well, (e.g., N-well 320 b), and therefore the body terminal of PMOS transistor M2, the body terminal of PMOS transistor M3, and the body terminal of PMOS transistor M4 are coupled together.

Each of the body terminal of PMOS transistor M2, the body terminal of PMOS transistor M3, the body terminal of PMOS transistor M4, the drain terminal of PMOS transistor M3 and the drain terminal of PMOS transistor M4 are coupled together at a node F1. In some embodiments, node F1 is electrically floating. In some embodiments, node F1 is electrically coupled to supply voltage VDD by PMOS transistors M1 and M3. In some embodiments, node F1 is electrically coupled to pad terminal PAD by PMOS transistors M2 and M4.

FIG. 3B is a circuit diagram of an equivalent circuit 300B of integrated circuit 300A, in accordance with some embodiments.

Equivalent circuit 300B is a variation of integrated circuit 300A showing parasitic elements 330 of integrated circuit 300A, and similar detailed description is therefore omitted. For example, equivalent circuit 300B corresponds to integrated circuit 300A of FIG. 3A with parasitic elements 330 (e.g., diode D1, parasitic transistors Q2 and Q3), in accordance with some embodiments.

Equivalent circuit 300B includes integrated circuit 300A and parasitic elements 330. Parasitic elements 330 include a diode D1, a parasitic transistor Q2 and a parasitic transistor Q3.

Each of an anode of the diode D1, the source terminal of PMOS transistor M3, the drain terminal of PMOS transistor M1, and an emitter of parasitic transistor Q3 are coupled together. Each of a cathode of the diode D1, the body terminal of PMOS transistor M1, the source terminal of PMOS transistor M1, the gate of PMOS transistor M2, the gate of PMOS transistor M4 and the first voltage supply VDD are coupled together. In some embodiments, diode D1 is forward biased, and is configured to allow a current flow through diode D1 and a parasitic current path. In some embodiments, diode D1 is reverse biased, and is configured to block a current from flowing through diode D1 and the parasitic current path.

Each of a base of parasitic transistor Q3, a collector of parasitic transistor Q3, a base of parasitic transistor Q2, a collector of parasitic transistor Q2, the drain terminal of PMOS transistor M3, the drain terminal of PMOS transistor M4, the body terminal of PMOS transistor M2, the body terminal of PMOS transistor M3, and the body terminal of PMOS transistor M4 are coupled together at node F1.

Each of an emitter of parasitic transistor Q2, the source terminal of PMOS transistor M2, the gate of PMOS transistor M1, the gate of PMOS transistor M3 and the pad terminal PAD are coupled together.

In some embodiments, during an ESD event with positive stress from the pad terminal PAD to the voltage supply VDD, the voltage of the pad terminal PAD is greater than the voltage of the voltage supply VDD, and therefore PMOS transistors M2 and M4 are turned on, and PMOS transistors M1 and M3 are turned off, and the voltage of the pad terminal PAD will be placed at node F1. In these embodiments, when the voltage of node F1 is equal to the voltage of the pad terminal PAD, the whole voltage stress of the ESD event will be placed across PMOS transistors M3 and M1, thereby turning on parasitic transistor Q3 and diode Q3 to conduct the discharged ESD current to the voltage supply VDD. Thus, since the ESD current path includes two parasitic elements (e.g., parasitic diode D1 and parasitic transistor Q3) positioned in different wells (320 a and 320 b), the ESD immunity is boosted compared to other approaches.

In some embodiments, during an ESD event with negative stress from the voltage supply VDD to the pad terminal PAD, the voltage of the voltage supply VDD is greater than the voltage of the pad terminal PAD, and therefore PMOS transistors M1 and M3 are turned on, and PMOS transistors M2 and M4 are turned off, and the voltage of the voltage supply VDD will be placed at node F1. In these embodiments, when the voltage of node F1 is equal to the voltage of the voltage supply VDD, the whole voltage stress of the ESD event will be placed across PMOS transistors M2 and M4, thereby turning on parasitic transistor Q2 to conduct the discharged ESD current to the pad terminal PAD. Thus, the ESD current path includes one parasitic element (e.g., parasitic transistor Q2).

In some embodiments, the 2-stacked PMOS structure utilizing PMOS transistors M2 and M4 can be reduced to a single PMOS transistor (either M2 or M4), if negative stress ESD events are not an issue.

FIG. 3C is a cross-sectional view of integrated circuit 300A, in accordance with some embodiments.

Integrated circuit 300C is an embodiment of integrated circuit 100B of FIG. 1B, and similar detailed description is therefore omitted.

Integrated circuit 300C illustrates an example of where PMOS transistor M1 is positioned in well 320 a, and PMOS transistors M2, M3 and M4 are positioned in well 320 b. In other words, wells NW2, NW3 and NW4 of FIG. 1B are merged into well 320 b.

Integrated circuit 300C comprises substrate 102, wells 320 a and 320 b, regions 304 a and 304 b, gates 106 a, 106 b, 106 c and 106 d, implant regions 308 a, 308 b, 308 c and 308 d, and implant regions 310 a, 310 b, 310 c and 310 d.

In comparison with integrated circuit 100B of FIG. 1B, well 320 a replaces well NW1, and well 320 b replaces wells NW2, NW3 and NW4 of FIG. 1B, and similar detailed description is therefore omitted. In other words, wells NW2, NW3 and NW4 of FIG. 1B are merged into well 320 b, and similar detailed description is therefore omitted. Well 320 b is different from well 320 a. Well 320 b is separated from well 320 a in the first direction X.

Gate 106 a is above well 320 a, and gates 106 b, 106 c and 106 d are above well 320 b. For ease of illustration, gates 106 a and 106 b are not shown as being coupled to each other or other elements, and gates 106 c and 106 d are not shown as being coupled to each other or other elements.

In comparison with integrated circuit 100B of FIG. 1B, region 304 a replaces region 104 a, and region 304 b replaces regions 104 b, 104 c and 104 d of FIG. 1B, and similar detailed description is therefore omitted. In other words, regions 104 b, 104 c, 104 d of FIG. 1B are merged into region 304 a, and similar detailed description is therefore omitted. Region 304 a is within well 320 a, and region 304 b is within well 320 b.

In comparison with integrated circuit 100B of FIG. 1B, implant regions 308 a, 308 b, 308 c and 308 d replace corresponding implant regions 108 a, 108 b, 108 c and 108 d, and implant regions 310 a, 310 b, 310 c and 310 d replace corresponding implant regions 110 a, 110 b, 110 c and 110 d, and similar detailed description is therefore omitted.

Implant regions 308 a and 310 a are within well 320 a. Implant regions 308 b, 308 c and 308 d and implant regions 310 b, 310 c and 310 d are within well 320 b.

Each of region 304 a, implant region 308 a and voltage supply VDD are electrically coupled together and corresponds to the connection between the body terminal of PMOS transistor M1, the source terminal of PMOS transistor M1 and the voltage supply VDD of FIG. 3A.

Implant region 310 a is electrically coupled to implant region 308 b and corresponds to the connection between the drain terminal of PMOS transistor M1 and the source terminal of PMOS transistor M3 of FIG. 3A.

Each of implant region 310 b, implant region 308 c and region 304 b are electrically coupled together at node F1, and corresponds to the connection between the drain terminal of PMOS transistor M3, the drain terminal of PMOS transistor M4 of FIG. 3A, the body terminal of PMOS transistor M2, the body terminal of PMOS transistor M3 and the body terminal of PMOS transistor M4 of FIG. 3A.

Implant region 310 c is electrically coupled to implant region 308 d and corresponds to the connection between the drain terminal of PMOS transistor M2 and the source terminal of PMOS transistor M4 of FIG. 3A.

Implant region 310 d is electrically coupled to the pad terminal PAD and corresponds to the connection between the source terminal of PMOS transistor M2 and the pad terminal PAD of FIG. 3A.

In comparison with integrated circuit 100B of FIG. 1B, parasitic diode D1 replaces parasitic pnp transistor 112 a of FIG. 1B, parasitic transistor Q3 replaces parasitic pnp transistor 112 b of FIG. 1B, and parasitic transistor Q2 replaces parasitic pnp transistors 112 c and 112 d of FIG. 1B, and similar detailed description is therefore omitted.

Parasitic diode D1 is formed by well 320 a and implant region 310 a. For example, implant region 310 a corresponds to the anode of diode D1, and well 320 a corresponds to the cathode of diode D1.

Parasitic transistor Q3 is formed by well 320 b, implant region 308 b and implant region 310 b. For example, the well 320 b forms a base of parasitic transistor Q3, the implant region 308 b forms an emitter of parasitic transistor Q3 and region 310 b forms a collector of parasitic transistor Q3.

Parasitic transistor Q2 is formed by well 320 b, implant region 308 c and implant region 310 d. For example, the well 320 b forms a base of parasitic transistor Q2, the implant region 310 d forms an emitter of parasitic transistor Q2 and region 308 c forms a collector of parasitic transistor Q2.

In some embodiments, by positioning PMOS transistor M1 in well 320 a, and by positioning PMOS transistors M2, M3 and M4 in a separate well (well 320 b), the parasitic current path of integrated circuit 300C includes parasitic elements (e.g., parasitic diode D1 and parasitic transistors Q2 and Q3) positioned in different wells (320 a and 320 b), thereby improving the ESD immunity of integrated circuit 300A-300C compared to other approaches, and integrated circuit 300A-300C occupies less area than other approaches with similar performance.

FIG. 4A is a circuit diagram of an integrated circuit 400A, in accordance with some embodiments. FIG. 4B is a circuit diagram of an equivalent circuit 400B of integrated circuit 400A, in accordance with some embodiments. FIG. 4C is a cross-sectional view of integrated circuit 400A, in accordance with some embodiments.

Integrated circuit 400A is an embodiment of integrated circuit 100A of FIG. 1A.

Integrated circuit 400A comprises PMOS transistors M1, M2, M3 and M4 coupled to the voltage supply VDD and the pad terminal PAD.

Integrated circuit 400A is a variation of integrated circuit 300A of FIG. 3A. In comparison with integrated circuit 300A of FIG. 3A, PMOS transistor M1 of integrated circuit 400A is positioned in well 320 a (FIG. 4C), PMOS transistors M3 and M4 of integrated circuit 400A are positioned in well 420 a (FIG. 4C), and PMOS transistor M2 of integrated circuit 400A is positioned in a well 420 b (FIG. 4C), and similar detailed description is therefore omitted. In some embodiments, each of wells 320 a, 420 a and 420 b are different from each other.

In comparison with integrated circuit 300A of FIG. 3A, PMOS transistor M2 of FIGS. 4A-4C is in well 420 b, and therefore the body terminal of PMOS transistor M2 is no longer coupled to the body terminal of PMOS transistor M3 and the body terminal of PMOS transistor M4. The body terminal of PMOS transistor M2 in FIGS. 4A-4C is coupled to node F2. In some embodiments, node F2 is charged from the pad terminal PAD by a parasitic body diode of PMOS transistor M4. In some embodiments, the parasitic body diode is formed between the gate and drain of PMOS transistor M4.

For example, in some embodiments, during an ESD event, the voltage of the pad terminal PAD is sufficient to cause the parasitic body diode to turn on and conduct resulting in node F2 charging to the voltage of the pad terminal PAD. Thus, in these embodiments, node F2 is able to track the voltage of the pad terminal PAD without being directly coupled to the body terminal of PMOS transistor M3 and the body terminal of PMOS transistor M4 nwell controller that means no PMOS/NMOS connected to F2. However, node F2 voltage could track to PAD by parasitic BJT. In some embodiments, a parasitic body diode is formed by implant 410 d and well 420 b. In some embodiments, a parasitic body diode is formed by implant 408 d and well 420 b.

PMOS transistors M3 and M4 are positioned in a same well, (e.g., well 420 a), and therefore the body terminal of PMOS transistor M3 and the body terminal of PMOS transistor M4 are coupled together. Each of the body terminal of PMOS transistor M3, the body terminal of PMOS transistor M4, the drain terminal of PMOS transistor M3 and the drain terminal of PMOS transistor M4 are coupled together at node F1. In some embodiments, node F1 is electrically floating. In some embodiments, node F1 is electrically coupled to supply voltage VDD by PMOS transistors M1 and M3. In some embodiments, node F1 is electrically coupled to pad terminal PAD by PMOS transistors M2 and M4.

FIG. 4B is a circuit diagram of an equivalent circuit 400B of integrated circuit 400A, in accordance with some embodiments.

Equivalent circuit 400B is a variation of integrated circuit 400A showing parasitic elements 430 of integrated circuit 400A, and similar detailed description is therefore omitted. For example, equivalent circuit 400B corresponds to integrated circuit 400A of FIG. 4A with parasitic elements 430 (e.g., diode D1, parasitic transistors Q2′, Q3 and Q4), in accordance with some embodiments.

Equivalent circuit 400B includes integrated circuit 400A and parasitic elements 430. Parasitic elements 430 are a variation of parasitic elements 330 of FIG. 3B, and similar detailed description is therefore omitted. Parasitic elements 430 include diode D1 of FIG. 3B, a parasitic transistor Q2′, parasitic transistor Q3 of FIG. 3B and a parasitic transistor Q4.

In comparison with parasitic elements 330 of FIGS. 3B-3C, parasitic transistor Q2′ and parasitic transistor Q4 replace parasitic transistor Q2 of FIG. 3B, and similar detailed description is therefore omitted.

In comparison with parasitic elements 330 of FIGS. 3B-3C, for FIG. 4B, each of the base of parasitic transistor Q3, the collector of parasitic transistor Q3, a base of parasitic transistor Q2′, a collector of parasitic transistor Q2′, the drain terminal of PMOS transistor M3, the drain terminal of PMOS transistor M4, the body terminal of PMOS transistor M3, and the body terminal of PMOS transistor M4 are coupled together at node F1.

In FIG. 4B, each of an emitter of parasitic transistor Q4, the source terminal of PMOS transistor M2, the gate of PMOS transistor M1, the gate of PMOS transistor M3 and the pad terminal PAD are coupled together. In FIG. 4B, a base of parasitic transistor Q4 is coupled to the body terminal of PMOS transistor M2.

In FIG. 4B, each of an emitter of parasitic transistor Q2′, a collector of parasitic transistor Q4, the drain terminal of PMOS transistor M2 and the source of PMOS transistor M4 are coupled together.

In some embodiments, during an ESD event with positive stress from the pad terminal PAD to the voltage supply VDD, the voltage of the pad terminal PAD is greater than the voltage of the voltage supply VDD, and therefore PMOS transistors M2 and M4 are turned on, and PMOS transistors M1 and M3 are turned off, and the voltage of the pad terminal PAD will be placed at node F1. In these embodiments, when the voltage of node F1 is equal to the voltage of the pad terminal PAD, the whole voltage stress of the ESD event will be placed across PMOS transistors M3 and M1, thereby turning on parasitic transistor Q3 and diode Q3 to conduct the discharged ESD current to the voltage supply VDD. Thus, since the parasitic current path includes two parasitic elements (e.g., parasitic diode D1 and parasitic transistor Q3) positioned in different wells (320 a and 420 a), the ESD immunity is boosted compared to other approaches.

In some embodiments, during an ESD event with negative stress from the voltage supply VDD to the pad terminal PAD, the voltage of the voltage supply VDD is greater than the voltage of the pad terminal PAD, and therefore PMOS transistors M1 and M3 are turned on, and PMOS transistors M2 and M4 are turned off, and the voltage of the voltage supply VDD will be placed at node F1. In these embodiments, when the voltage of node F1 is equal to the voltage of the voltage supply VDD, the whole voltage stress of the ESD event will be placed across PMOS transistors M2 and M4, thereby turning on parasitic transistors Q2′ and Q4 to conduct the discharged ESD current to the pad terminal PAD. Thus, since the ESD current path includes two parasitic elements (e.g., parasitic transistor Q4 and parasitic transistor Q2′) positioned in different wells (420 a and 420 b), the ESD immunity is boosted compared to other approaches.

FIG. 4C is a cross-sectional view of integrated circuit 400A, in accordance with some embodiments.

Integrated circuit 400C is an embodiment of integrated circuit 100B of FIG. 1B or integrated circuit 300B of FIG. 3B, and similar detailed description is therefore omitted.

Integrated circuit 400C illustrates an example of where PMOS transistor M1 is positioned in well 320 a, PMOS transistors M3 and M4 are positioned in well 420 a, and PMOS transistor M2 is positioned in well 420 b. In comparison with integrated circuit 100B of FIG. 1B, wells NW3 and NW4 of FIG. 1B are merged into well 420 a.

Integrated circuit 400C comprises substrate 102, wells 320 a, 420 a and 420 b, regions 304 a, 304 b and 404 d, gates 106 a, 106 b, 106 c and 106 d, implant regions 308 a, 408 b, 408 c and 408 d, and implant regions 310 a, 410 b, 410 c and 410 d.

In comparison with integrated circuit 100B of FIG. 1B, well 320 a replaces well NW1, and well 420 a replaces wells NW3 and NW2 of FIG. 1B, and well 420 b replaces wells NW1 of FIG. 1B, and similar detailed description is therefore omitted. In other words, wells NW2 and NW3 of FIG. 1B are merged into well 420 a, and similar detailed description is therefore omitted. Each of wells 320 a, 420 a and 420 b are separated from each other in the first direction X. In some embodiments, each of wells 320 a, 420 a and 420 b are different from each other.

Gate 106 a is above well 320 a, gates 106 b and 106 c are above well 420 a and gate 106 d is above well 420 b. For ease of illustration, gates 106 a and 106 b are not shown as being coupled to each other or other elements, and gates 106 c and 106 d are not shown as being coupled to each other or other elements.

In comparison with integrated circuit 100B of FIG. 1B, region 404 b replaces regions 104 b and 104 c of FIG. 1B, and region 404 d replaces regions 104 d of FIG. 1B, and similar detailed description is therefore omitted. Stated differently, regions 104 b and 104 c of FIG. 1B are merged into region 404 b, and similar detailed description is therefore omitted. Region 304 a is within well 320 a, region 404 b is within well 420 a and region 404 d is within well 420 b.

Integrated circuit 400C is a variation of integrated circuit 300C of FIG. 3C, and similar detailed description is therefore omitted. In comparison with integrated circuit 300C of FIG. 3C, implant regions 408 b, 408 c and 408 d replace corresponding implant regions 308 b, 308 c and 308 d, and implant regions 410 b, 410 c and 410 d replace corresponding implant regions 310 b, 310 c and 310 d, and similar detailed description is therefore omitted.

Implant regions 408 b and 408 c and implant regions 410 b and 410 c are within well 420 a. Implant region 408 d and implant region 410 d are within well 420 b.

Implant region 310 a is electrically coupled to implant region 408 b and corresponds to the connection between the drain terminal of PMOS transistor M1 and the source terminal of PMOS transistor M3 of FIG. 4A.

Each of implant region 410 b, implant region 408 c and region 404 b are electrically coupled together at node F1, and corresponds to the connection between the drain terminal of PMOS transistor M3, the drain terminal of PMOS transistor M4 of FIG. 4A, the body terminal of PMOS transistor M3 and the body terminal of PMOS transistor M4.

Region 404 d is electrically coupled to node F2, and corresponds to the connection between the body terminal of PMOS transistor M2 and node F2 in FIG. 4A.

Implant region 410 c is electrically coupled to implant region 408 d and corresponds to the connection between the drain terminal of PMOS transistor M2 and the source terminal of PMOS transistor M4 of FIG. 4A.

Implant region 410 d is electrically coupled to the pad terminal PAD and corresponds to the connection between the source terminal of PMOS transistor M2 and the pad terminal PAD of FIG. 4A.

Integrated circuit 400C includes parasitic diode D1 of FIG. 3C, a parasitic transistor Q2′, parasitic transistor Q3 of FIG. 3C and a parasitic transistor Q4. In comparison with integrated circuit 300C of FIG. 3C, parasitic transistor Q2′ and parasitic transistor Q4 replace parasitic Q2 of FIG. 3C, and similar detailed description is therefore omitted.

In comparison with integrated circuit 100B of FIG. 1B, parasitic transistor Q2′ replaces parasitic pnp transistor 112 c of FIG. 1B, and parasitic transistor Q4 replaces parasitic pnp transistor 112 d of FIG. 1B, and similar detailed description is therefore omitted.

Parasitic transistor Q2′ is formed by well 420 a, implant region 408 c and implant region 410 c. For example, the well 420 a forms a base of parasitic transistor Q2′, the implant region 410 c forms an emitter of parasitic transistor Q2′ and region 408 c forms a collector of parasitic transistor Q2′.

Parasitic transistor Q4 is formed by well 420 b, implant region 408 d and implant region 410 d. For example, the well 420 b forms a base of parasitic transistor Q4, the implant region 410 d forms an emitter of parasitic transistor Q4 and region 408 d forms a collector of parasitic transistor Q4.

In some embodiments, by positioning PMOS transistor M1 in well 320 a, by positioning PMOS transistors M3 and M4 in a separate well (well 420 a), and by positioning PMOS transistor M2 in another separate well (well 420 b), a parasitic current path of integrated circuit 400C includes parasitic elements (e.g., parasitic diode D1 and parasitic transistor Q3) positioned in different wells (320 a and 420 a), and another parasitic current path of integrated circuit 400C includes parasitic elements (e.g., parasitic transistors Q2′ and Q4) positioned in different wells (420 a and 420 b), thereby improving the ESD immunity of integrated circuit 400A-400C compared to other approaches, and integrated circuit 400A-400C occupies less area than other approaches with similar performance.

FIG. 5A is a circuit diagram of an integrated circuit 500A, in accordance with some embodiments. FIG. 5B is a circuit diagram of an equivalent circuit 500B of integrated circuit 500A, in accordance with some embodiments. FIG. 5C is a cross-sectional view of integrated circuit 500A, in accordance with some embodiments.

Integrated circuit 500A is an embodiment of integrated circuit 200A of FIG. 2A, and similar detailed description is therefore omitted. In comparison with integrated circuit 200A of FIG. 2A, PMOS transistor M1 is positioned in well 320 a (FIG. 5C), PMOS transistor M3 is positioned in a well 520 a (FIG. 5C), and PMOS transistors M2, M4, M5 and M6 are positioned in a well 520 b (FIG. 5C). In some embodiments, each of wells 320 a, 520 a and 520 b are separated from each other and are thus different.

Integrated circuit 500A comprises PMOS transistors M1, M2, M3, M4, M5 and M6 coupled to the voltage supply VDD and the pad terminal PAD.

Integrated circuit 500A is a variation of integrated circuit 400A of FIG. 4A, and similar detailed description is therefore omitted.

PMOS transistors M2, M4, M5 and M6 are positioned in a same well, (e.g., well 520 b). Each of the body terminal of PMOS transistor M2, the body terminal of PMOS transistor M4, the body terminal of PMOS transistor M5, the body terminal of PMOS transistor M6, the drain terminal of PMOS transistor M5 and the drain terminal of PMOS transistor M6 are coupled together at node F1. In some embodiments, node F1 is electrically floating. In some embodiments, node F1 is electrically coupled to supply voltage VDD by PMOS transistors M1, M3 and M5. In some embodiments, node F1 is electrically coupled to pad terminal PAD by PMOS transistors M2 M4 and M6.

PMOS transistor M3 is positioned in well 520 a. In FIGS. 5A-5C and 6A-6C, a body terminal of PMOS transistor M3, the drain terminal of PMOS transistor M3, and the source terminal of PMOS transistor M5 are coupled together at a node F2′. In some embodiments, by coupling the body terminal of PMOS transistor M3 to the drain terminal of PMOS transistor M3, PMOS transistor M3 is self-biased and node F2′ is not provided a bias voltage from a circuit external of integrated circuit 500A.

FIG. 5B is a circuit diagram of an equivalent circuit 500B of integrated circuit 500A, in accordance with some embodiments.

Equivalent circuit 500B is a variation of integrated circuit 500A showing parasitic elements 530 of integrated circuit 500A, and similar detailed description is therefore omitted. For example, equivalent circuit 500B corresponds to integrated circuit 500A of FIG. 5A with parasitic elements 530 (e.g., diode D1, parasitic transistors Q2″, Q3 and Q5), in accordance with some embodiments.

Equivalent circuit 500B is a variation of equivalent circuit 300B of FIG. 3B or 400B of FIG. 4B, and similar detailed description is therefore omitted.

Equivalent circuit 500B includes integrated circuit 500A and parasitic elements 530. Parasitic elements 530 include diode D1, a parasitic transistor Q2″, parasitic transistor Q3 and a parasitic transistor Q5.

Each of the gate of PMOS transistor M6, the cathode of the diode D1, the body terminal of PMOS transistor M1, the source terminal of PMOS transistor M1, the gate of PMOS transistor M2, the gate of PMOS transistor M4, and the first voltage supply VDD are coupled together.

For FIGS. 5A-5C & 6A-6C, each of an emitter of parasitic transistor Q5, the base of parasitic transistor Q3, the collector of parasitic transistor Q3, the drain terminal of PMOS transistor M3 and the source terminal of PMOS transistor M5 are coupled together.

For FIGS. 5A-5C, each of a collector of parasitic transistor Q5, a base of parasitic transistor Q5, the body terminal of PMOS transistor M5, the drain terminal of PMOS transistor M5, the drain terminal of PMOS transistor M6, the body terminal of PMOS transistor M6, the body terminal of PMOS transistor M4, the body terminal of PMOS transistor M2, a collector of parasitic transistor Q2″ and a base of parasitic transistor Q2″ are coupled together at node F1.

Each of an emitter of parasitic transistor Q2″, the gate of PMOS transistor M5, the source terminal of PMOS transistor M2, the gate of PMOS transistor M1, the gate of PMOS transistor M3 and the pad terminal PAD are coupled together.

In some embodiments, during an ESD event with positive stress from the pad terminal PAD to the voltage supply VDD, the voltage of the pad terminal PAD is greater than the voltage of the voltage supply VDD, and therefore PMOS transistors M2, M4 and M6 are turned on, and PMOS transistors M1, M3 and M5 are turned off, and the voltage of the pad terminal PAD will be placed at node F1. In these embodiments, when the voltage of node F1 is equal to the voltage of the pad terminal PAD, the whole voltage stress of the ESD event will be placed across PMOS transistors M5, M3 and M1, thereby turning on parasitic transistors Q5 and Q3 and diode Q3 to conduct the discharged ESD current to the voltage supply VDD. Thus, since the ESD current path includes three parasitic elements (e.g., parasitic diode D1, parasitic transistor Q3 and parasitic transistor Q5) positioned in different wells (320 a, 520 a and 520 b), the ESD immunity is boosted compared to other approaches.

In some embodiments, during an ESD event with negative stress from the voltage supply VDD to the pad terminal PAD, the voltage of the voltage supply VDD is greater than the voltage of the pad terminal PAD, and therefore PMOS transistors M1 M3, and M5 are turned on, and PMOS transistors M2, M4 and M6 are turned off, and the voltage of the voltage supply VDD will be placed at node F1. In these embodiments, when the voltage of node F1 is equal to the voltage of the voltage supply VDD, the whole voltage stress of the ESD event will be placed across PMOS transistors M2, M4 and M6, thereby turning on parasitic transistor Q2″ to conduct the discharged ESD current to the pad terminal PAD. Thus, the ESD current path includes one parasitic element (e.g., parasitic transistor Q2″).

In some embodiments, the 3-stacked PMOS structure utilizing PMOS transistors M2, M4 and M6 can be reduced to a single PMOS transistor (one of M2, M4 or M6) or a 2-stacked PMOS structure utilizing two PMOS transistors (two of M2, M4 or M6), if negative stress ESD events are not an issue.

FIG. 5C is a cross-sectional view of integrated circuit 500A, in accordance with some embodiments.

Integrated circuit 500C is an embodiment of integrated circuit 200B of FIG. 2B, and similar detailed description is therefore omitted.

Integrated circuit 500C illustrates an example of PMOS transistor M1 positioned in well 320 a, PMOS transistor M3 is positioned in well 520 a, and PMOS transistors M2, M4, M5 and M6 are positioned in well 520 b. In some embodiments, each of wells 320 a, 520 a and 520 b are separated from each other and are thus different.

Integrated circuit 500C comprises substrate 102, wells 320 a, 520 a and 520 b, regions 304 a, 504 b and 504 c, gates 106 a, 106 b, 106 c, 106 d, 206 e and 206 f, implant regions 308 a, 508 b, 508 c, 508 d, 508 e and 508 f, and implant regions 310 a, 510 b, 510 c, 510 d, 510 e and 510 f.

In comparison with integrated circuit 200B of FIG. 2B, well 320 a replaces well NW4, well 520 a replaces well NW3, and well 520 b replaces wells NW5, NW6, NW2 and NW1 of FIG. 2B, and similar detailed description is therefore omitted.

In other words, wells NW5, NW6, NW2 and NW1 of FIG. 2B are merged into well 520 b, and similar detailed description is therefore omitted. Each of well 320 a, 520 a and 520 b are separated from each other in the first direction X. In some embodiments, at least well 320 a, 520 a or 520 b is different from another of at least well 320 a, 520 a or 520 b.

Gate 106 a is above well 320 a, gate 106 b is above well 520 a, and gates 106 b, 106 c, 106 d, 206 e and 206 f are above well 520 b. For ease of illustration, gates 106 a, 106 b and 206 e are not shown as being coupled to each other or other elements, and gates 106 c, 106 d and 206 f are not shown as being coupled to each other or other elements.

In comparison with integrated circuit 200B of FIG. 2B, region 304 a replaces region 104 a, region 504 b replaces region 104 b of FIG. 2B, and region 504 c replaces regions 104 c, 104 d, 204 e and 204 f of FIG. 2B, and similar detailed description is therefore omitted. Stated differently, regions 104 c, 104 d, 204 e and 204 f of FIG. 2B are merged into region 504 b, and similar detailed description is therefore omitted. Region 304 a is within well 320 a, region 504 b is within well 520 a and region 504 c is within well 520 b.

Integrated circuit 500C is a variation of integrated circuit 300C of FIG. 3C, and similar detailed description is therefore omitted. In comparison with integrated circuit 300C of FIG. 3C, implant regions 408 b, 408 c and 408 d replace corresponding implant regions 308 b, 308 c and 308 d, and implant regions 410 b, 410 c and 410 d replace corresponding implant regions 310 b, 310 c and 310 d, and similar detailed description is therefore omitted. Implant regions 308 a and 310 a are described in FIG. 3C, and similar detailed description is therefore omitted.

In comparison with integrated circuit 200B of FIG. 2B, implant regions 508 b, 508 c, 508 d, 508 e and 508 f replace corresponding implant regions 108 b, 108 c, 108 d, 208 e and 208 f, and implant regions 510 b, 510 c, 510 d, 510 e and 510 f replace corresponding implant regions 110 b, 110 c, 110 d, 210 e and 210 f, and similar detailed description is therefore omitted.

Implant regions 308 a and 310 a are within well 320 a. Implant regions 508 b and 510 b are within well 520 a. Implant regions 508 c, 508 d, 508 e and 508 f and implant regions 510 c, 510 d, 510 e and 510 f are within well 520 b.

Implant region 310 a is electrically coupled to implant region 508 b and corresponds to the connection between the drain terminal of PMOS transistor M1 and the source terminal of PMOS transistor M3 of FIG. 5A.

Each of region 504 c, implant region 510 e and implant region 508 f are electrically coupled together at node F1, and corresponds to the connection between the body terminal of PMOS transistor M5, the drain terminal of PMOS transistor M5, the drain terminal of PMOS transistor M6, the body terminal of PMOS transistor M6, the body terminal of PMOS transistor M4, and the body terminal of PMOS transistor M2 at node F1.

Each of region 504 b, implant region 510 b and implant region 508 e are electrically coupled together at node F2′, and corresponds to the connection between the body terminal of PMOS transistor M3, the drain terminal of PMOS transistor M3 and the source terminal of PMOS transistor M5 of FIG. 5A.

Implant region 510 f is electrically coupled to implant region 508 c and corresponds to the connection between the source terminal of PMOS transistor M6 and the drain terminal of PMOS transistor M4 of FIG. 5A.

Implant region 510 c is electrically coupled to implant region 508 d and corresponds to the connection between the source terminal of PMOS transistor M4 and the drain terminal of PMOS transistor M2 of FIG. 5A.

Implant region 510 d is electrically coupled to the pad terminal PAD and corresponds to the connection between the source terminal of PMOS transistor M2 and the pad terminal PAD of FIG. 5A.

Integrated circuit 500C includes parasitic diode D1 of FIG. 3C, a parasitic transistor Q2″, parasitic transistor Q3 of FIG. 3C and a parasitic transistor Q5. Parasitic diode D1 is described in FIG. 3C, and parasitic transistor Q3 is described in FIG. 3C, and similar detailed description is therefore omitted.

In comparison with integrated circuit 200B of FIG. 2+B, parasitic transistor Q2″ replaces parasitic pnp transistors 212 f, 112 c and 112 d of FIG. 2B, and parasitic transistor Q5 replaces parasitic pnp transistor 212 e of FIG. 2B, and similar detailed description is therefore omitted.

Parasitic transistor Q3 in FIG. 5C is formed by well 520 a, implant region 508 b and implant region 510 b. For example, the well 520 a forms the base of parasitic transistor Q3 in FIG. 5C, the implant region 508 b forms the emitter of parasitic transistor Q3 in FIG. 5C and region 510 b forms the collector of parasitic transistor Q3 in FIG. 5C.

Parasitic transistor Q2″ is formed by well 520 b, implant region 508 f and implant region 510 d. For example, the well 520 b forms a base of parasitic transistor Q2″, the implant region 510 d forms an emitter of parasitic transistor Q2″ and region 508 f forms a collector of parasitic transistor Q2″.

Parasitic transistor Q5 is formed by well 520 b, implant region 508 e and implant region 510 e. For example, the well 520 b forms a base of parasitic transistor Q5, the implant region 508 e forms an emitter of parasitic transistor Q5 and region 510 e forms a collector of parasitic transistor Q5.

In some embodiments, by positioning PMOS transistor M1 in well 320 a, by positioning PMOS transistor M3 in a separate well (well 520 a), and by positioning PMOS transistors M5, M6, M4 and M2 in another separate well (well 520 b), a parasitic current path of integrated circuit 500C includes parasitic elements (e.g., parasitic diode D1, parasitic transistor Q3 and parasitic transistor Q5) positioned in different wells (320 a, 520 a and 520 b), and another parasitic current path of integrated circuit 500C includes parasitic elements (e.g., parasitic transistor Q2″) positioned in the another well (520 b), thereby improving the ESD immunity of integrated circuit 500A-500C compared to other approaches, and integrated circuit 500A-500C occupies less area than other approaches with similar performance.

FIG. 6A is a circuit diagram of an integrated circuit 600A, in accordance with some embodiments. FIG. 6B is a circuit diagram of an equivalent circuit 600B of integrated circuit 600A, in accordance with some embodiments. FIG. 6C is a cross-sectional view of integrated circuit 600A, in accordance with some embodiments.

Integrated circuit 600A is an embodiment of integrated circuit 200A of FIG. 2A.

Integrated circuit 600A comprises PMOS transistors M1, M2, M3, M4, M5 and M6 coupled to the voltage supply VDD and the pad terminal PAD.

Integrated circuit 600A is a variation of integrated circuit 500A of FIG. 5A and integrated circuit 400A of FIG. 4A. In comparison with integrated circuit 500A of FIG. 5A or integrated circuit 400A of FIG. 4A, PMOS transistor M1 of integrated circuit 600A is positioned in well 320 a (FIG. 6C), PMOS transistor M3 of integrated circuit 600A is positioned in well 520 a (FIG. 6C), PMOS transistor M2 of integrated circuit 600A is positioned in well 420 b (FIG. 6C), and PMOS transistors M4, M5 and M6 of integrated circuit 600A are positioned in a well 620 a (FIG. 6C), and similar detailed description is therefore omitted.

In some embodiments, each of wells 320 a, 420 a and 420 b are different from each other.

In comparison with integrated circuit 500A of FIG. 5A, PMOS transistor M2 of FIGS. 6A-6C is in well 420 b and the body terminal of PMOS transistor M2 is coupled to node F2. In some embodiments, node F2 is charged from the pad terminal PAD by the parasitic body diode of PMOS transistor M4.

The configuration of PMOS transistor M1 in FIGS. 6A-6C is similar to the configurations of PMOS transistor M1 in at least FIGS. 3A-3C, and similar detailed description is therefore omitted. The configuration of PMOS transistor M3 in FIGS. 6A-6C is similar to the configurations of PMOS transistor M3 in at least FIGS. 5A-5C, and similar detailed description is therefore omitted.

PMOS transistors M4, M5 and M6 are positioned in a same well (e.g., well 620 a). Each of the body terminal of PMOS transistor M4, the body terminal of PMOS transistor M5, the body terminal of PMOS transistor M6, the drain terminal of PMOS transistor M5 and the drain terminal of PMOS transistor M6 are coupled together at node F1 in FIGS. 6A-6C. In some embodiments, node F1 is electrically floating. In some embodiments, node F1 is electrically coupled to supply voltage VDD by PMOS transistors M1, M3 and M5. In some embodiments, node F1 is electrically coupled to pad terminal PAD by PMOS transistors M2, M4 and M6.

FIG. 6B is a circuit diagram of an equivalent circuit 600B of integrated circuit 600A, in accordance with some embodiments.

Equivalent circuit 600B is a variation of integrated circuit 600A showing parasitic elements 630 of integrated circuit 600A, and similar detailed description is therefore omitted. For example, equivalent circuit 600B corresponds to integrated circuit 600A of FIG. 6A with parasitic elements 630 (e.g., diode D1, parasitic transistors Q2′″, Q3, Q4 and Q5), in accordance with some embodiments.

Equivalent circuit 600B is a variation of equivalent circuit 500B of FIG. 5B or 400B of FIG. 4B, and similar detailed description is therefore omitted.

Equivalent circuit 600B includes integrated circuit 600A and parasitic elements 630. Parasitic elements 630 include diode D1, parasitic transistor Q2′″, parasitic transistor Q3, parasitic transistor Q4 and parasitic transistor Q5.

The configuration of diode D1, parasitic transistor Q3, and parasitic transistor Q5 in FIGS. 6A-6C is similar to the configurations of diode D1, parasitic transistor Q3, and parasitic transistor Q5 in at least FIGS. 5A-5C, and similar detailed description is therefore omitted.

For FIGS. 6A-6C, each of the collector of parasitic transistor Q5, the base of parasitic transistor Q5, the body terminal of PMOS transistor M5, the drain terminal of PMOS transistor M5, the drain terminal of PMOS transistor M6, the body terminal of PMOS transistor M6, the body terminal of PMOS transistor M4, the collector of parasitic transistor Q2′″ and the base of parasitic transistor Q2′″ are coupled together at node F1.

For FIGS. 6A-6C, each of an emitter of parasitic transistor Q4, the gate of PMOS transistor M5, the source terminal of PMOS transistor M2, the gate of PMOS transistor M1, the gate of PMOS transistor M3 and the pad terminal PAD are coupled together.

For FIGS. 6A-6C, the body terminal of PMOS transistor M2 is coupled to base of parasitic transistor Q4.

For FIGS. 6A-6C, each of the drain terminal of PMOS transistor M2, the source terminal of PMOS transistor M4, the collector of parasitic transistor Q4 and the emitter of parasitic transistor Q2′″ are coupled together.

In some embodiments, during an ESD event with positive stress from the pad terminal PAD to the voltage supply VDD, the voltage of the pad terminal PAD is greater than the voltage of the voltage supply VDD, and therefore PMOS transistors M2, M4 and M6 are turned on, and PMOS transistors M1, M3 and M5 are turned off, and the voltage of the pad terminal PAD will be placed at node F1. In these embodiments, when the voltage of node F1 is equal to the voltage of the pad terminal PAD, the whole voltage stress of the ESD event will be placed across PMOS transistors M5, M3 and M1, thereby turning on parasitic transistors Q5′ and Q3 and diode Q3 to conduct the discharged ESD current to the voltage supply VDD. Thus, since the ESD current path includes three parasitic elements (e.g., parasitic diode D1, parasitic transistor Q3 and parasitic transistor Q5′) positioned in different wells (320 a, 520 a and 620 a), the ESD immunity is boosted compared to other approaches.

In some embodiments, during an ESD event with negative stress from the voltage supply VDD to the pad terminal PAD, the voltage of the voltage supply VDD is greater than the voltage of the pad terminal PAD, and therefore PMOS transistors M1 M3, and M5 are turned on, and PMOS transistors M2, M4 and M6 are turned off, and the voltage of the voltage supply VDD will be placed at node F1. In these embodiments, when the voltage of node F1 is equal to the voltage of the voltage supply VDD, the whole voltage stress of the ESD event will be placed across PMOS transistors M2, M4 and M6, thereby turning on parasitic transistors Q2′″ and Q4 to conduct the discharged ESD current to the pad terminal PAD. Thus, since the parasitic current path includes two parasitic elements (e.g., parasitic transistor Q4 and parasitic transistor Q2′″) positioned in different wells (420 b and 620 a), the ESD immunity is boosted compared to other approaches.

In some embodiments, the 2-stacked PMOS structure in a same well (well 620 a) utilizing PMOS transistors M2 and M6 can be reduced to a single PMOS transistor (one of M2 or M6), if negative stress ESD events are not an issue.

FIG. 6C is a cross-sectional view of integrated circuit 600A, in accordance with some embodiments.

Integrated circuit 600C is an embodiment of integrated circuit 200B of FIG. 2B, and similar detailed description is therefore omitted.

Integrated circuit 600C illustrates an example of PMOS transistor M1 positioned in well 320 a, PMOS transistor M3 is positioned in well 520 a, PMOS transistor M2 is positioned in well 420 b, and PMOS transistors M4, M5 and M6 are positioned in a well 620 a, and similar detailed description is therefore omitted. In some embodiments, each of wells 320 a, 420 b, 520 a and 620 a are separated from each other in the first direction X and are thus different.

Integrated circuit 600C comprises substrate 102, wells 320 a, 420 b, 520 a and 620 a, regions 304 a, 404 d, 504 b and 604 c, gates 106 a, 106 b, 106 c, 106 d, 206 e and 206 f, implant regions 308 a, 408 d, 508 b, 608 c, 608 e and 608 f, and implant regions 310 a, 410 d, 510 b, 610 c, 610 e and 610 f.

In comparison with integrated circuit 200B of FIG. 2B, well 320 a replaces well NW4, well 420 b replaces well NW1, well 520 a replaces well NW3, and well 620 a replaces wells NW5, NW6 and NW2 of FIG. 2B, and similar detailed description is therefore omitted.

In other words, wells NW5, NW6 and NW2 of FIG. 2B are merged into well 620 a, and similar detailed description is therefore omitted. Each of well 320 a, 420 b, 520 a and 620 a are separated from each other in the first direction X. In some embodiments, at least well 320 a, 420 b, 520 a or 620 a is different from another of at least well 320 a, 420 b, 520 a or 620 a.

Gate 106 a is above well 320 a, gate 106 b is above well 520 a, gates 106 c, 206 e and 206 f are above well 620 a, and gate 106 d is above well 420 b. For ease of illustration, gates 106 a, 106 b and 206 e are not shown as being coupled to each other or other elements, and gates 106 c, 106 d and 206 f are not shown as being coupled to each other or other elements.

In comparison with integrated circuit 200B of FIG. 2B, region 304 a replaces region 104 a, region 504 b replaces region 104 b of FIG. 2B, region 604 c replaces regions 104 c, 204 e and 204 f of FIG. 2B, and region 404 d replaces region 104 d of FIG. 2B, and similar detailed description is therefore omitted.

Stated differently, regions 104 c, 204 e and 204 f of FIG. 2B are merged into region 604 c, and similar detailed description is therefore omitted. Region 304 a is within well 320 a, region 504 b is within well 520 a, region 404 d is within well 420 b, and region 604 c is within well 620 a.

Integrated circuit 600C is a variation of integrated circuit 500C of FIG. 5C and integrated circuit 400C of FIG. 4C, and similar detailed description is therefore omitted. In comparison with integrated circuit 500C of FIG. 5C, implant regions 608 e, 608 f and 608 c replace corresponding implant regions 508 e, 508 f and 508 c, and implant regions 610 e, 610 f and 610 c replace corresponding implant regions 510 e, 510 f and 510 c, and similar detailed description is therefore omitted.

Implant regions 308 a and 310 a are described in FIG. 3C, and similar detailed description is therefore omitted. Implant regions 508 b and 510 b are described in FIG. 5C, and similar detailed description is therefore omitted.

Integrated circuit 600C is a variation of integrated circuit 400C of FIG. 4C, and similar detailed description is therefore omitted. For example, implant regions 408 d and 410 d described in FIG. 4C, and similar detailed description is therefore omitted.

In comparison with integrated circuit 200B of FIG. 2B, implant regions 608 e, 608 f and 608 c replace corresponding implant regions 108 e, 108 f and 108 c, and implant regions 610 e, 610 f and 610 c replace corresponding implant regions 110 e, 110 f and 110 c, and similar detailed description is therefore omitted.

Implant regions 308 a and 310 a are within well 320 a. Implant regions 508 b and 510 b are within well 520 a. Implant region 408 d and implant region 410 d are within well 420 b. Implant regions 608 c, 608 e and 608 f and implant regions 610 c, 610 e and 610 f are within well 520 b.

Each of region 604 c, implant region 610 e and implant region 608 f are electrically coupled together at node F1, and corresponds to the connection between the body terminal of PMOS transistor M5, the drain terminal of PMOS transistor M5, the drain terminal of PMOS transistor M6, the body terminal of PMOS transistor M6, and the body terminal of PMOS transistor M4 at node F1.

Each of region 504 b, implant region 510 b and implant region 608 e are electrically coupled together at node F2′, and corresponds to the connection between the body terminal of PMOS transistor M3, the drain terminal of PMOS transistor M3 and the source terminal of PMOS transistor M5 of FIG. 6A.

Implant region 404 d is electrically coupled to node F2 and corresponds to the connection between the body terminal of PMOS transistor M2 and node F2 of FIG. 6A.

Implant region 610 f is electrically coupled to implant region 608 c and corresponds to the connection between the source terminal of PMOS transistor M6 and the drain terminal of PMOS transistor M4 of FIG. 6A.

Implant region 610 c is electrically coupled to implant region 408 d and corresponds to the connection between the source terminal of PMOS transistor M4 and the drain terminal of PMOS transistor M2 of FIG. 6A.

Implant region 410 d is electrically coupled to the pad terminal PAD and corresponds to the connection between the source terminal of PMOS transistor M2 and the pad terminal PAD of FIG. 5A.

Integrated circuit 600C includes parasitic diode D1 of FIG. 3C, a parasitic transistor Q2′″, parasitic transistor Q3 of FIG. 3C, parasitic transistor Q4 of FIG. 4C, and a parasitic transistor Q5′.

Parasitic diode D1 is described in FIG. 3C, and parasitic transistor Q3 is described in FIGS. 3C and 5C, parasitic transistor Q4 is described in FIG. 4C, and similar detailed description is therefore omitted.

In comparison with integrated circuit 200B of FIG. 2B, parasitic transistor Q2′″ replaces parasitic pnp transistors 212 f and 112 c of FIG. 2B, and similar detailed description is therefore omitted.

In comparison with integrated circuit 500C of FIG. 5C, parasitic transistor Q5′ replaces parasitic transistor Q5 of FIG. 5C, and similar detailed description is therefore omitted.

Parasitic transistor Q5′ is formed by well 620 a, implant region 608 e and implant region 610 e. For example, the well 620 a forms a base of parasitic transistor Q5′, the implant region 608 e forms an emitter of parasitic transistor Q5 and region 610 e forms a collector of parasitic transistor Q5.

Parasitic transistor Q2′″ is formed by well 620 a, implant region 608 f and implant region 610 c. For example, the well 620 a forms a base of parasitic transistor Q2′″, the implant region 610 c forms an emitter of parasitic transistor Q2′″ and region 608 f forms a collector of parasitic transistor Q2′″.

In some embodiments, by positioning PMOS transistor M1 in well 320 a, by positioning PMOS transistor M3 in a separate well (well 520 a), by positioning PMOS transistors M5, M6 and M4 in another separate well (well 620 a), and by positioning PMOS transistor M2 in yet another separate well (well 420 b), a parasitic current path of integrated circuit 600C includes parasitic elements (e.g., parasitic diode D1, parasitic transistor Q3 and parasitic transistor Q5′) positioned in different wells (320 a, 520 a and 620 a), and another parasitic current path of integrated circuit 600C includes parasitic elements (e.g., parasitic transistor Q2′″ and parasitic transistor Q4) positioned in different wells (620 a and 420 b), thereby improving the ESD immunity of integrated circuit 600A-600C compared to other approaches, and integrated circuit 600A-600C occupies less area than other approaches with similar performance.

FIG. 7A is a circuit diagram of an integrated circuit 700A, in accordance with some embodiments.

Integrated circuit 700A is an embodiment of integrated circuit 100A of FIG. 1A. Integrated circuit 700A is a variation of integrated circuit 300A of FIG. 3A, and similar detailed description is therefore omitted. In comparison with integrated circuit 300A of FIG. 3A, integrated circuit 700A further comprises a control logic circuit 702 a.

Control logic circuit 702 a is configured to generate a control logic signal CLS. In some embodiments, the control logic signal CLS is similar to the voltage of the pad terminal PAD, and similar detailed description is therefore omitted.

In comparison with integrated circuit 300A of FIG. 3A, each of the gate terminal of PMOS transistor M3 and the gate terminal of PMOS transistor M1 are not coupled to the source terminal of PMOS transistor M2 and the pad terminal PAD.

In FIGS. 7A-7B, the gate terminal of PMOS transistor M3 and the gate terminal of PMOS transistor M1 are coupled to the control logic circuit 702 a, and are configured to receive a control logic signal CLS from the control logic circuit 702 a.

In some embodiments, the control logic signal CLS is equal to a logic 0 corresponding to a reference supply voltage VSS. In some embodiments, the control logic signal CLS is equal to a logic 1 corresponding to the voltage of the pad terminal PAD (e.g., the PAD voltage).

FIG. 7B is a circuit diagram of an integrated circuit 700B, in accordance with some embodiments.

Integrated circuit 700B is an embodiment of integrated circuit 100A of FIG. 1A. Integrated circuit 700B is a variation of integrated circuit 400A of FIG. 4A, and similar detailed description is therefore omitted. In comparison with integrated circuit 400A of FIG. 4A, integrated circuit 700B further comprises control logic circuit 702 a. The control logic circuit 702 a of FIG. 7B was described in FIG. 7A, and similar detailed description is therefore omitted.

In comparison with integrated circuit 400A of FIG. 4A, each of the gate terminal of PMOS transistor M3 and the gate terminal of PMOS transistor M1 are not coupled to the source terminal of PMOS transistor M2 and the pad terminal PAD.

In FIG. 7B, the gate terminal of PMOS transistor M3 and the gate terminal of PMOS transistor M1 are coupled to the control logic circuit 702 a, and are configured to receive a control logic signal CLS from the control logic circuit 702 a.

FIG. 7C is a circuit diagram of an integrated circuit 700C, in accordance with some embodiments.

Integrated circuit 700C is an embodiment of integrated circuit 200A of FIG. 2A. Integrated circuit 700C is a variation of integrated circuit 500A of FIG. 5A, and similar detailed description is therefore omitted. In comparison with integrated circuit 500A of FIG. 5A, integrated circuit 700C further comprises a control logic circuit 702 b.

Control logic circuit 702 b of FIGS. 7C-7D is similar to control logic circuit 702 a described in FIGS. 7A-7B, and similar detailed description is therefore omitted.

In comparison with integrated circuit 500A of FIG. 5A, each of the gate terminal of PMOS transistor M3, the gate terminal of PMOS transistor M1 and the gate terminal of PMOS transistor M5 are not coupled to the source terminal of PMOS transistor M2 and the pad terminal PAD.

In FIGS. 7C-7D, the gate terminal of PMOS transistor M3, the gate terminal of PMOS transistor M1 and the gate terminal of PMOS transistor M5 are coupled to the control logic circuit 702 b, and are configured to receive control logic signal CLS from the control logic circuit 702 b.

FIG. 7D is a circuit diagram of an integrated circuit 700D, in accordance with some embodiments.

Integrated circuit 700D is an embodiment of integrated circuit 200A of FIG. 2A. Integrated circuit 700D is a variation of integrated circuit 600A of FIG. 6A, and similar detailed description is therefore omitted. In comparison with integrated circuit 600A of FIG. 6A, integrated circuit 700D further comprises control logic circuit 702 b.

Control logic circuit 702 b of FIG. 7D is similar to control logic circuit 702 a described in FIGS. 7A-7B, and similar detailed description is therefore omitted.

In comparison with integrated circuit 600A of FIG. 6A, each of the gate terminal of PMOS transistor M3, the gate terminal of PMOS transistor M1 and the gate terminal of PMOS transistor M5 are not coupled to the source terminal of PMOS transistor M2 and the pad terminal PAD.

In FIG. 7D, the gate terminal of PMOS transistor M3, the gate terminal of PMOS transistor M1 and the gate terminal of PMOS transistor M5 are coupled to the control logic circuit 702 b, and are configured to receive control logic signal CLS from the control logic circuit 702 b.

FIG. 8 is a circuit diagram of a control logic circuit 800, in accordance with some embodiments.

Control logic circuit 800 is an embodiment of at least control logic circuit 700A of FIG. 7A, control logic circuit 700B of FIG. 7B, control logic circuit 700C of FIG. 7C or control logic circuit 700D of FIG. 7D.

Control logic circuit 800 includes a PMOS transistor M7 and a NMOS transistor M8 coupled to voltage supply VDD, pad terminal PAD, reference voltage supply VSS and a node NA. In some embodiments, control logic circuit 800 is an inverter. Other circuits are within the scope of the present disclosure.

A source terminal of PMOS transistor M7 is coupled to at least the pad terminal PAD and is configured to receive a pad voltage (not labelled). Each of a gate terminal of PMOS transistor M7 and a gate terminal of NMOS transistor M8 is coupled together. The gate terminal of PMOS transistor M7 and NMOS transistor M8 are further coupled to at least the voltage supply VDD, and are configured to receive the supply voltage (not labelled). A drain terminal of PMOS transistor M7 is coupled to a drain terminal of NMOS transistor M8 at node NA. A source terminal of PMOS transistor M8 is coupled to reference voltage supply VSS.

In some embodiments, when the voltage of the pad terminal PAD is greater than a voltage of the supply voltage VDD, then PMOS transistor M7 is turned on and pulls node NA to the voltage of the pad terminal PAD thereby causing the voltage of node NA to be equal to the voltage of the pad terminal PAD, and the control logic signal CLS is equal to a logic 1. In some embodiments, when the voltage of the pad terminal PAD is less than a voltage of the supply voltage VDD, then NMOS transistor M8 is turned on and pulls node NA to the voltage of the reference supply voltage VSS thereby causing the voltage of node NA to be equal to the voltage of the reference supply voltage VSS, and the control logic signal CLS is equal to a logic 0.

Method

FIG. 9 is a flowchart of a method of operating a circuit, such as the integrated circuit of FIG. 1A-1B, 2A-2B, 3A-3C, 4A-4C, 5A-5C, 6A-6C, 7A-7D or 8, in accordance with some embodiments. It is understood that additional operations may be performed before, during, and/or after the method 900 depicted in FIG. 9, and that some other processes may only be briefly described herein. It is understood that method 900 utilizes features of one or more of integrated circuits 100A-100B of FIGS. 1A-1B, 200A-200B of FIGS. 2A-2B, 300A-300C of FIGS. 3A-3C, 400A-400C of FIGS. 4A-4C, 500A-500C of FIGS. 5A-5C, 600A-600C of FIGS. 6A-6C, 700A-700C of FIGS. 7A-7D or 800 of FIG. 8.

In operation 902 of method 900, a pad voltage is received on a pad voltage terminal PAD. In some embodiments, the pad voltage is greater than a supply voltage of a voltage supply VDD. In some embodiments, if the pad voltage is greater than the supply voltage of the voltage supply VDD, then method 900 proceeds to operation 904.

In some embodiments, the pad voltage is less than the supply voltage of a voltage supply VDD. In some embodiments, if the pad voltage is less than the supply voltage of the voltage supply VDD, then method 900 proceeds to operation 912.

In operation 904 of method 900, at least a first set of transistors M2 coupled to the pad voltage terminal are turned on in response to the pad voltage being greater than the supply voltage of the voltage supply VDD, and at least a second set of transistors coupled to the first voltage supply are turned off in response to the pad voltage being greater than the supply voltage of the voltage supply VDD. In some embodiments, the first set of transistors includes at least PMOS transistor M1, M3 or M5. In some embodiments, the second set of transistors includes at least PMOS transistor M2, M4 or M6. In some embodiments, a first transistor of the first set of transistors is in a first well, and a second transistor of the second set of transistors is in a second well different from the first well. In some embodiments, the first well includes at least a well described in FIGS. 1A-8, the second well includes at least another well described in FIGS. 1A-8.

In some embodiments, operation 904 comprises one or more of operations 906, 908 or 910.

In operation 906 of method 900, a first node F1 is electrically coupled with the pad voltage terminal by the first set of transistors.

In operation 908 of method 900, the first node F1 is electrically decoupled from the first voltage supply by the second set of transistors.

In operation 910 of method 900, the pad voltage is placed across the second set of transistors.

In operation 912 of method 900, at least the first set of transistors M2 coupled to the pad voltage terminal are turned off in response to the pad voltage being less than the supply voltage of the voltage supply VDD, and at least the second set of transistors coupled to the first voltage supply are turned on in response to the pad voltage being less than the supply voltage of the voltage supply VDD.

In some embodiments, operation 912 comprises one or more of operations 914, 916 or 918.

In operation 914 of method 900, the first node F1 is electrically decoupled from the pad voltage terminal by the first set of transistors.

In operation 916 of method 900, the first node F1 is electrically coupled with the first voltage supply by the second set of transistors.

In operation 918 of method 900, the pad voltage is placed across the first set of transistors.

In some embodiments, one or more of the operations of method 900 is not performed. While method 900 was described above with reference to FIGS. 3A-3C, it is understood that method 900 utilizes the features of one or more of FIGS. 1A-2B & 4A-8. In these embodiments, other operations of method 900 would be performed consistent with the description and operation of integrated circuits 100A-200B & 400A-800 of FIGS. 1A-2B & 4A-8.

Furthermore, various PMOS transistors shown in FIGS. 1A-8 are of a particular dopant type (e.g., N-type or P-type) and are for illustration purposes. Embodiments of the disclosure are not limited to a particular transistor type, and one or more of the PMOS or NMOS transistors shown in FIGS. 1A-8 can be substituted with a corresponding transistor of a different transistor/dopant type. Similarly, the low or high logical value of various signals used in the above description is also used for illustration. Embodiments of the disclosure are not limited to a particular logical value when a signal is activated and/or deactivated. Selecting different logical values is within the scope of various embodiments. Selecting different numbers of PMOS transistors in 1A-8 is within the scope of various embodiments.

One aspect of this description relates to a voltage tracking circuit. The voltage tracking circuit includes a first transistor, a second transistor, a third transistor and a fourth transistor. In some embodiments, the first transistor in a first well, and the first transistor including a first gate terminal, a first drain terminal and a first source terminal, the first source terminal being coupled to a first voltage supply, the first gate terminal being coupled to a pad voltage terminal and configured to receive a pad voltage. In some embodiments, the second transistor including a second gate terminal, a second drain terminal and a second source terminal, the second source terminal being coupled to the first drain terminal, the second gate terminal being coupled to the first gate terminal and the pad voltage terminal. In some embodiments, the third transistor including a third gate terminal, a third drain terminal and a third source terminal, the third gate terminal being coupled to the first voltage supply. In some embodiments, the fourth transistor including a fourth gate terminal, a fourth drain terminal and a fourth source terminal, the fourth drain terminal being coupled to the third source terminal, the fourth gate terminal being coupled to the third gate terminal and the first voltage supply, and the fourth source terminal being coupled to the pad voltage terminal. In some embodiments, at least the third transistor is in a second well different from the first well, and being separated from the first well in a first direction.

Another aspect of this description relates to a voltage tracking circuit. The voltage tracking circuit includes a control logic circuit, a first transistor, a second transistor, a third transistor and a fourth transistor. In some embodiments, the first transistor is in a first well, and the first transistor including a first gate terminal, a first drain terminal and a first source terminal, the first source terminal being coupled to a first voltage supply, the first gate terminal being coupled to the control logic circuit and configured to receive a control logic signal. In some embodiments, the second transistor including a second gate terminal, a second drain terminal and a second source terminal, the second source terminal being coupled to the first drain terminal, the second gate terminal being coupled to the first gate terminal and the control logic circuit, and configured to receive the control logic signal. In some embodiments, the third transistor including a third gate terminal, a third drain terminal and a third source terminal, the third gate terminal being coupled to the first voltage supply. In some embodiments, the fourth transistor including a fourth gate terminal, a fourth drain terminal and a fourth source terminal, the fourth drain terminal being coupled to the third source terminal, the fourth gate terminal being coupled to the third gate terminal and the first voltage supply, and the fourth source terminal being coupled to a pad voltage terminal. In some embodiments, at least the third transistor is in a second well different from the first well, and being separated from the first well in a first direction.

Yet another aspect of this description relates to a method of operating a pad voltage tracking circuit. The method includes receiving a pad voltage on a pad voltage terminal PAD, the pad voltage being greater than a supply voltage VDD of a first voltage supply; turning on at least a first set of transistors M2 coupled to the pad voltage terminal, and turning off a second set of transistors coupled to the first voltage supply, a first transistor of the first set of transistors being in a first well, and a second transistor of the second set of transistors being in a second well different from the first well; electrically coupling a first node with the pad voltage terminal by the first set of transistors; electrically decoupling the first node from the first voltage supply by the second set of transistors; and placing the pad voltage across the second set of transistors.

A number of embodiments have been described. It will nevertheless be understood that various modifications may be made without departing from the spirit and scope of the disclosure. For example, various transistors being shown as a particular dopant type (e.g., N-type or P-type Metal Oxide Semiconductor (NMOS or PMOS)) are for illustration purposes. Embodiments of the disclosure are not limited to a particular type. Selecting different dopant types for a particular transistor is within the scope of various embodiments. The low or high logical value of various signals used in the above description is also for illustration. Various embodiments are not limited to a particular logical value when a signal is activated and/or deactivated. Selecting different logical values is within the scope of various embodiments. In various embodiments, a transistor functions as a switch. A switching circuit used in place of a transistor is within the scope of various embodiments. In various embodiments, a source of a transistor can be configured as a drain, and a drain can be configured as a source. As such, the term source and drain are used interchangeably. Various signals are generated by corresponding circuits, but, for simplicity, the circuits are not shown.

Various figures show capacitive circuits using discrete capacitors for illustration. Equivalent circuitry may be used. For example, a capacitive device, circuitry or network (e.g., a combination of capacitors, capacitive elements, devices, circuitry, or the like) can be used in place of the discrete capacitor. The above illustrations include exemplary steps, but the steps are not necessarily performed in the order shown. Steps may be added, replaced, changed order, and/or eliminated as appropriate, in accordance with the spirit and scope of disclosed embodiments.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A voltage tracking circuit comprising: a first transistor in a first well, the first transistor including a first gate terminal, a first drain terminal and a first source terminal, the first source terminal being coupled to a first voltage supply, the first gate terminal being coupled to a pad voltage terminal and configured to receive a pad voltage; a second transistor including a second gate terminal, a second drain terminal and a second source terminal, the second source terminal being coupled to the first drain terminal, the second gate terminal being coupled to the first gate terminal and the pad voltage terminal; a third transistor including a third gate terminal, a third drain terminal and a third source terminal, the third gate terminal being coupled to the first voltage supply; and a fourth transistor including a fourth gate terminal, a fourth drain terminal and a fourth source terminal, the fourth drain terminal being coupled to the third source terminal, the fourth gate terminal being coupled to the third gate terminal and the first voltage supply, and the fourth source terminal being coupled to the pad voltage terminal, wherein at least the third transistor is in a second well different from the first well, and the second well is separated from the first well in a first direction.
 2. The voltage tracking circuit of claim 1, wherein the first transistor further includes a first body terminal coupled to the first voltage supply and the first source terminal; the second transistor further includes a second body terminal; the third transistor further includes a third body terminal; the fourth transistor further includes a fourth body terminal; each of the second body terminal, the third body terminal, the fourth body terminal, the second drain terminal and the third drain terminal are coupled together; and the second transistor, the third transistor and the fourth transistor are in the second well.
 3. The voltage tracking circuit of claim 1, wherein the second transistor is in the second well; and the fourth transistor is in a third well different from the first well and the second well, and the third well is separated from the first well and the second well in the first direction.
 4. The voltage tracking circuit of claim 3, wherein the first transistor further includes a first body terminal coupled to the first voltage supply and the first source terminal; the second transistor further includes a second body terminal; the third transistor further includes a third body terminal; the fourth transistor further includes a fourth body terminal coupled to a node; each of the second body terminal, the third body terminal, the second drain terminal and the third drain terminal are coupled together.
 5. The voltage tracking circuit of claim 1, further comprising: a fifth transistor including a fifth gate terminal, a fifth drain terminal and a fifth source terminal, the fifth source terminal being coupled to the second drain terminal, the fifth gate terminal being coupled to the first gate terminal, the second gate terminal and the pad voltage terminal; and a sixth transistor including a sixth gate terminal, a sixth drain terminal and a sixth source terminal, the sixth source terminal being coupled to the third drain terminal, the sixth gate terminal being coupled to the third gate terminal, the fourth gate terminal and the first voltage supply, and the sixth drain terminal being coupled to the fifth drain terminal, wherein the fifth transistor and the sixth transistor are in the second well; and the second transistor is in a third well different from the first well and the second well, and being separated from the first well and the second well in the first direction.
 6. The voltage tracking circuit of claim 5, wherein the fourth transistor is in the second well.
 7. The voltage tracking circuit of claim 6, wherein the first transistor further includes a first body terminal coupled to the first voltage supply and the first source terminal; the second transistor further includes a second body terminal; the third transistor further includes a third body terminal; the fourth transistor further includes a fourth body terminal coupled to a node; the fifth transistor further includes a fifth body terminal; the sixth transistor further includes a sixth body terminal; each of the third body terminal, the fourth body terminal, the fifth body terminal, the sixth body terminal, the fifth drain terminal and the sixth drain terminal are coupled together; and the second body terminal is coupled to a node, the second drain terminal and the fifth source terminal.
 8. The voltage tracking circuit of claim 5, wherein the fourth transistor is in a fourth well different from the first well, the second well and the third well, and is separated from the first well, the second well and the third well in the first direction.
 9. The voltage tracking circuit of claim 8, wherein the first transistor further includes a first body terminal coupled to the first voltage supply and the first source terminal; the second transistor further includes a second body terminal; the third transistor further includes a third body terminal; the fourth transistor further includes a fourth body terminal coupled to a node; the fifth transistor further includes a fifth body terminal; the sixth transistor further includes a sixth body terminal; each of the third body terminal, the fifth body terminal, the sixth body terminal, the fifth drain terminal and the sixth drain terminal are coupled together; and the second body terminal is coupled to a node, the second drain terminal and the fifth source terminal; and the fourth body terminal is coupled to another node.
 10. A voltage tracking circuit comprising: a control logic circuit; a first transistor in a first well, the first transistor including a first gate terminal, a first drain terminal and a first source terminal, the first source terminal being coupled to a first voltage supply, the first gate terminal being coupled to the control logic circuit and configured to receive a control logic signal; a second transistor including a second gate terminal, a second drain terminal and a second source terminal, the second source terminal being coupled to the first drain terminal, the second gate terminal being coupled to the first gate terminal and the control logic circuit, and configured to receive the control logic signal; a third transistor including a third gate terminal, a third drain terminal and a third source terminal, the third gate terminal being coupled to the first voltage supply; and a fourth transistor including a fourth gate terminal, a fourth drain terminal and a fourth source terminal, the fourth drain terminal being coupled to the third source terminal, the fourth gate terminal being coupled to the third gate terminal and the first voltage supply, and the fourth source terminal being coupled to a pad voltage terminal, wherein at least the third transistor is in a second well different from the first well, and being separated from the first well in a first direction.
 11. The voltage tracking circuit of claim 10, wherein the control logic circuit comprises an inverter configured to receive an inverted control logic signal and to generate the control logic signal.
 12. The voltage tracking circuit of claim 10, wherein the first transistor further includes a first body terminal coupled to the first voltage supply and the first source terminal; the second transistor further includes a second body terminal; the third transistor further includes a third body terminal; the fourth transistor further includes a fourth body terminal; each of the second body terminal, the third body terminal, the fourth body terminal, the second drain terminal and the third drain terminal are coupled together; the second transistor and the fourth transistor are in the second well; and the third drain terminal is coupled to the second drain terminal.
 13. The voltage tracking circuit of claim 10, wherein the second transistor is in the second well; the fourth transistor is in a third well different from the first well and the second well, and is separated from the first well and the second well in the first direction; and the third drain terminal is coupled to the second drain terminal.
 14. The voltage tracking circuit of claim 13, wherein the first transistor further includes a first body terminal coupled to the first voltage supply and the first source terminal; the second transistor further includes a second body terminal; the third transistor further includes a third body terminal; the fourth transistor further includes a fourth body terminal coupled to a node; and each of the second body terminal, the third body terminal, the second drain terminal and the third drain terminal are coupled together.
 15. The voltage tracking circuit of claim 10, further comprising: a fifth transistor including a fifth gate terminal, a fifth drain terminal and a fifth source terminal, the fifth source terminal being coupled to the second drain terminal, the fifth gate terminal being coupled to the first gate terminal, the second gate terminal and the control logic circuit, and configured to receive the control logic signal; and a sixth transistor including a sixth gate terminal, a sixth drain terminal and a sixth source terminal, the sixth source terminal being coupled to the third drain terminal, the sixth gate terminal being coupled to the third gate terminal, the fourth gate terminal and the first voltage supply, and the sixth drain terminal being coupled to the fifth drain terminal, wherein the fifth transistor and the sixth transistor are in the second well; and the second transistor is in a third well different from the first well and the second well, and being separated from the first well and the second well in the first direction.
 16. The voltage tracking circuit of claim 15, wherein the fourth transistor is in the second well.
 17. The voltage tracking circuit of claim 16, wherein the first transistor further includes a first body terminal coupled to the first voltage supply and the first source terminal; the second transistor further includes a second body terminal; the third transistor further includes a third body terminal; the fourth transistor further includes a fourth body terminal coupled to a node; the fifth transistor further includes a fifth body terminal; the sixth transistor further includes a sixth body terminal; each of the third body terminal, the fourth body terminal, the fifth body terminal, the sixth body terminal, the fifth drain terminal and the sixth drain terminal are coupled together; and the second body terminal is coupled to a node, the second drain terminal and the fifth source terminal.
 18. The voltage tracking circuit of claim 15, wherein the fourth transistor is in a fourth well different from the first well, the second well and the third well, and is separated from the first well, the second well and the third well in the first direction.
 19. The voltage tracking circuit of claim 18, wherein the first transistor further includes a first body terminal coupled to the first voltage supply and the first source terminal; the second transistor further includes a second body terminal; the third transistor further includes a third body terminal; the fourth transistor further includes a fourth body terminal coupled to a node; the fifth transistor further includes a fifth body terminal; the sixth transistor further includes a sixth body terminal; each of the third body terminal, the fifth body terminal, the sixth body terminal, the fifth drain terminal and the sixth drain terminal are coupled together; and the second body terminal is coupled to a node, the second drain terminal and the fifth source terminal; and the fourth body terminal is coupled to another node.
 20. A method of operating a pad voltage tracking circuit, comprising: receiving a pad voltage on a pad voltage terminal PAD, the pad voltage being greater than a supply voltage VDD of a first voltage supply; turning on at least a first set of transistors M2 coupled to the pad voltage terminal, and turning off a second set of transistors coupled to the first voltage supply, a first transistor of the first set of transistors being in a first well, and a second transistor of the second set of transistors being in a second well different from the first well; electrically coupling a first node with the pad voltage terminal by the first set of transistors; electrically decoupling the first node from the first voltage supply by the second set of transistors; and placing the pad voltage across the second set of transistors. 